The invention relates to a spiral steamer for fabric webs in which there is a housing that is sealed except for an intake and-an outlet, having means for producing and maintaining a steam atmosphere in the housing, deflecting rollers mounted to rotate in the housing, transversely to the fabric web, which are arranged in such a way that the fabric web can be guided around the outside of the deflecting rollers in a spiral that has several windings. The steamer also has a turning device arranged in the center of the spiral, by which the fabric web can be guided laterally out of the spiral, to the outlet.
Such spiral steamers are described, for example, in the book by Peter and Rouette, xe2x80x9cGrundlagen der Textilveredlungxe2x80x9d [Principles of Textile Finishing], 13th edition (1989), Deutsche Fachverlag GmbH Frankfurt am Main, on page 665, and illustrated in FIG. 7.288. The individual windings of the spiral, viewed in a vertical lengthwise plane of the fabric web, have approximately the shape of a horizontal ellipsis, whose longer axis runs approximately horizontally. The fabric web is passed around the deflecting rollers on the outside, in each instance. In the bottom segments, the fabric web is held against the deflecting rollers solely by its lengthwise tension. Sometimes, it hangs freely. In any case, however, in the known spiral steamers, the tension of the fabric web at the deflecting rollers located in the region of the apex at the ends of the horizontal axis of the elliptical spiral windings (these are the apices that are meant when the term xe2x80x9capexxe2x80x9d is used hereinafter) is significantly greater than at the lowest point of the winding in question. The high tension in the region of the apices is undesirable, for one thing because many materials cannot tolerate it, because the treatment effect becomes non-uniform due to the bending of the deflecting rollers at that location, and because under some circumstances, particularly in the initial region, a squeezing effect can occur, causing parts of the metered bath applied to the fabric web to be removed from it.
The invention is based on the task of making the tension in the fabric web uniform in a spiral steamer of the type noted above.
In the present invention, the fabric web hangs down, in its bottom segment, between the apices of the spiral winding, and is held against the deflecting rollers only by its tension. The flatter the bottom segment runs, the greater are the contact forces at the deflecting rollers in the vicinity of the apices in relation to the contact surfaces in the region of the lowest point. If the fabric web between the deflecting rollers, in the region of the apices, is now compared with a hanging chain or a hanging rope, without the deflecting rollers it would run in a certain parabola-like curve that is referred to as a chain line or a catenary curve, and is independent of the weight of the chain or the rope per length unit.
If, as happens in the invention, the deflecting rollers are now arranged in such a way that the track of the fabric web in a vertical lengthwise plane of the web approximately corresponds to a chain line or catenary curve, no special tension in the fabric web is required in order to have it rest against all of the deflecting rollers, even in the bottom segment of the winding of the fabric web in each instance. This makes the lengthwise tension that is required in the web to achieve the desired contact force lower, in total, on the one hand, and more uniform, on the other hand.
To avoid the formation of condensate and dye deposits on the deflecting rollers, they are all driven. Until now, this drive was provided via chains. Since a spiral steamer can contain over a hundred deflecting rollers, the mechanical effort involved in providing the chain drive was significant.
According to another aspect of the invention, each deflecting roller has its own drive assigned to it, e.g. via an electric motor.
In other words, the drive torque is no longer mechanically passed on from a drive motor, common to several deflecting rollers, to additional deflecting rollers.
With this provision of a suitable control system, what is achieved is that the tension of the fabric web is checked at several locations and regulated in suitable manner. The tension of the fabric web is expressed as a specific force exerted by the fabric web on a deflecting roller, which force can be measured by a suitable transducer. One of the drives of the deflecting rollers of a group is the master drive, regulated on the basis of the measurement taken at a deflecting roller of this group, and the other drives follow it. The deflecting roller with the master drive and the deflecting roller with the measurement can be the same deflecting roller, but do not have to be.
In this manner, a uniform and relatively low lengthwise tension can be maintained in the entire fabric content of the spiral steamer.
A further measure to maintain a low fabric web tension, which is actually known, is drive of the deflecting rollers with peripheral precession.
In steamers, steam constantly exits at the intake of the fabric web, resulting in a significant loss of energy and corresponding costs.
A further aspect of this invention is a channel to serve to reduce the steam losses. This channel, with its changes in cross-section in the region of the incoming fabric web, acts similar to a labyrinth seal, and inhibits the outflow of steam along the fabric web at the intake.
It is true that this structure is particularly practical for the spiral steamer according to the present invention, which has large dimensions when the fabric content is large, but it can also be used for other types of steamers.